The field of absorbable biomaterials has been dominated by the use of purified, naturally occurring polymers such as collagen and thermoplastic polyesters based on five common lactone monomers (glycolide, L-lactide, p-dioxanone, trimethylene carbonate, and ε-caprolactone). Homopolymers and simple copolymers of these monomers adequately met the physical and mechanical property requirements of the first absorbable sutures and meshes. Then, polymeric blends and segmented block copolymers were developed to address the need to control more precisely not only the physical and mechanical properties of the fibers, but also the in vivo breaking strength retention profile and total absorption of these materials. In general, the majority of these polymers are strong, stiff thermoplastics that are processed by injection molding, extrusion, and other common melt processing techniques.
Recently, absorbable thermoplastic elastomers have been developed to address the need in medical device development for an elastic material, e.g. U.S. Pat. Nos. 5,468,253 and 5,713,920. In addition, absorbable polymeric liquids and pastes have been developed to increase the range of physical properties exhibited by the aliphatic polyesters based on glycolide, lactide, p-dioxanone, 5,5-dimethyl-1,3-dioxan-2-one, trimethylene carbonate, and ε-caprolactone, e.g. U.S. Pat. Nos. 5,411,554, 5,599,852, 5,631,015, 5,653,992, 5,688,900, 5,728,752 and 5,824,333.
Hubbell et al., in U.S. Pat. Nos. 5,573,934 and 5,858,746, disclosed the use of photocurable polymers to encapsulate biological materials including drugs, proteins, and cells in a hydrogel. The hydrogel was formed from a water soluble biocompatible macromer containing at least two free radical polymerizable substituents and either a thermal or light activated free radical initiator. An example of such a photoreactive system is an acrylate ester endcapped poly(ethylene glycol) containing ethyl eosin and a tertiary amine. After a series of light activated reactions between ethyl eosin and the amine, the acrylate endgroups polymerize into short segments that result in a crosslinked polymeric network composed of poly(ethylene glycol) chains radiating outward from the acrylate oligomers. The physical and mechanical properties of the resulting hydrogel are dependent on the reproducibility of the free radical oligomerization reaction.
Hubbell et al. expanded this concept in U.S. Pat. No. 5,410,016 in the form of photocurable, segmented block copolymers composed not only of water soluble segments, such as poly(ethylene glycol), but also of segments with hydrolizable groups, in particular, with short segments of aliphatic polyesters. In this way, the resulting hydrogel breaks down into soluble units in vitro and in vivo in a controlled fashion. The photochemistry is the same and based on the free radical polymerization of acrylate and methacrylate endgroups.
Despite these developments in the field of absorbable biomaterials, there is a need for thermosetting materials, that is, materials that can be easily applied as low molecular weight compounds, and by a controlled chemical process, crosslink to form a polymeric network having physical, mechanical and biological properties determined by its components.
Thus, it is an objective of the present invention to provide a photocurable, absorbable, thermosetting polymer for use in medical applications and drug delivery.